Amplifier with muting means



May 13, 1952 N. FEINl-:R ETAL AMPLIFIER WITH MUTING MEANS Filed Nov. 4, 1949 Patented May 13, 1952 AMPLIFIER WITH MUTING MEANS Nathaniel Feiner and Samuel H. Gershater, Chicago, Ill., assignors to Functional Music, Inc., Chicago, Ill., a corporation of Illinois Application November 4, 1949, Serial No. 125,424

3 Claims. 1

This invention relates to amplifiers and particularly to electronic amplifiers that are utilized in association with radio receivers and the like.

In connection with radio broadcasting, it has been proposed to derive additional revenue from broadcasting operations by affording specialized service to restaurants, bars, retail stores and the like so that the commercial announcements that are broadcast may be eliminated in such retail lestablishments so as to thereby afford purely musical entertainment in such establishments.

In such instances it has been proposed that the amplifiers be governed by means responsive to an inaudible signal impressed on the carrier Wave either as a subsonic or a supersonic signal, but in accordance with the arrangements heretofore suggested, it has been necessary to use a continuous control signal during the entire period covered by the commercial announcement. It is, therefore, an important object of the present invention to enable such control of an amplifier to be attained by means that are relatively simple and inexpensive in character, and which are responsive to relatively short control signals. More specifically, it is an object of the present invention to enable such control to be attained by means that are electronic in character in all of the elements thereof, and a related object is to enable such control to `be attained by relatively short .start and stop signals which are of different frequencies. l

Other and further objects `of the present invention will be apparent from the following description and claims ,and are illustrated in the accompanying drawing which, by way of illustration, shows a preferred embodiment of the present invention and the principle thereof and whatwe new consider to be the best ,mode in which we have contemplated applying that principle. Other embodiments of the invention embodying the same or equivalent principle may be used and structural changes may be made as desired by those skilled inthe art without departing from the present invention.

In the drawing, the single gure constitutes a schematic wiring diagram illustrating an amplifier embodying the features of `the invention.

For purposes of disclosure, the invention is herein illustrated as embodied in an amplifier having a main amplifying tube ID, and control means including a pair of control amplifying tubes I I and I2 and a rectifying tube I3 associated with the main amplifying tube ID in such a way that the main amplifying tube I0 may be rendered conductive or non-conductive at will through the application of inaudible control signals to the tube I2. The main amplifying tube I 0 and the control amplifying tube I2 are, as

` herein shown, associated with a signal source such asa radio receiver I 5, so that the program signal and the control signals are derived, after detection, from the common source as represented by the radio receiver I5. As herein shown, the signal from the `radio receiver I5 is amplified through a single stage of amplification by the amplifying tube I0, this tube having an anode IOA, a cathode IUC and a control grid IIJG. The grid IOG is connected through a wire I6, a condenser II and a `wire I8 to the radio receiver I5 so as to receive the signal output from the radio receiver, and the amplified output of the tube I0 is transmitted to the audio output by means including an audio `output connection I l9. As herein shown, the audio output connection is connected through a resistance 20 to a positive B- voltage source, as at 2 I, and from theconnection 2|, a resistor 22 is connected to the cathode IUC. The cathode IUC is also connected through resisters 23, 24 and 25 in series to ground. as indicated at 26.

Between the resistors 23 and 24, a wire 21 is extended so as to be connected to one end of a resistor 28, the other end of which is connected to a resistor 29, which in turnhas its other end connected to the grid IDG. At the juncture of the Wire 21 with the resistor 28,'anaudio bypass condenser 3D has one of its terminals connected, the other terminal being connected to ground as at 3 I.

The control tube II has an anode IIA, a cathode II'C and a control grid I IG, and the anode IIA is connected by wires 32 and 33 in .series to the juncture of the resistors 28 and 29. The Wire 33` is also connected to one terminal of a condenser 34, the other terminal of which is connected to ground as at 35. The cathode IIC is connected by wires 36 and -31 in series to the cathode I3C of the rectifying tube I3, and a Wire 38 extends from the wire 36 to the juncture of the resistors24 and 25.

The control tube II has a fixed value positive `voltage applied thereto at all times, and this is accomplished by connecting resistors 40 and 4I in 4Vseries from the grid IIG to a positive B- voltage source as indicated at 42, the juncture of the resistors 40 and 4I being connected through a resistor 43 to ground as indicated at 441.

The output of the radio receiver I5 is also applied to the control grid of the amplifer tube I2, this tube lI2 having an anode IZA, a cathode I2C and a control grid I2G, and the output of the radio receiver I5 beingapplied to the grid I2G through a wire 46 a condenser 31 and. a wire 48 in series. The cathode I2C is connected to the ground at 49 and a bias resistor 50 is connected between the cathode and the grid. The -anode or plate I v2A is connected by a wire 5| to a terminal 52, this terminal being connected through a resistor 53 to a positive B-voltage 3 source, as indicated at 54. The terminal 52 is connected by a wire 55, a condenser 56 and a Wire 51 in series to the grid IIG of the control tube Il.

The rectifying tube I3 has an anode I3A, a grid I3G and a cathode I3C, it being noted that the cathode I3C is connected by the wires 31 and the terminal 60 and ground at 6I.

The anode I3A is connected by wires 65 and 61 and a resistance 68 in series to one terminal of a tank circuit 10, this'A tank circuit being connected at its other end or terminal by wire 'I3 to the grid IIG of the control tube II. The end of the tank circuit 10 that is connected to the resistor 68 is also connected through a condenser 14 to ground at 15, and a resistance 16 is connected between the wire 61 and the terminal of the condenser 14 that is connectedto ground at 15.

While the circuits may be varied in many ways in accordance With known practice While at the same time utilizing the novel control of the amplifier as taught by the present invention, and while the values of the circuit components may be varied widely in accordance with known practice, we have found that highly satisfactory results are obtained by utilizing circuit components according toY the following table of identifying designations and values:

Triode IIl-one-half of a 6L'1Y tube Triode II--other half of the 6L1 tube Triode I2triode section of a 6SL'1 tube Diode I3-diode-connected other section of the 6SL7 tube Resistorf 20 ohms 240,000 22 do 240,000 23 do 1,200 24 do 47,000 25 do 20,000 28 do 500,000 29 do 500,000 40 do 500,000 4 I megohms 1.2 43 ohms 100,000 50 megohms 1.0 53 ohms 240,000 6a do 240,000 16 do 240,000 Condenser- I1 microfarads-- .01 30 d0 4.0 34 do .1 41 micromicrofarads 50. 56 do 15 58 do 50 59 do 500 14 microfarads 0.1 Tankcircuit 62 resonant at 35 kilocycles Tank circuit 10 resonant at 20 kilocycles It will be recognized, of course, that the signal output of the radio receiver I5 will be applied at all times to the grids of the tubes I and I2, and the amplified output of the tube I2 is arranged in accordance with the frequency of the received inaudible control signal, as will be described in some detail hereinafter, to govern the conductivity of the control tube II, the association of the control tube II with the grid IDG of the amplifier tube I0 being such that when the control tube II is non-conductive, the amplifying tube I0 will be in a conductive condition so that the signal from the radio receiver I will be amplified and transmitted to the audio output. The signal from the receiver I5 may be said to be normally amplified by the amplifier tube IIJ, the bias afforded by the resistor 23 being effective under normal conditions to afford a grid'bias which renders the tube I0 conductive. When the amplifier tube I'D is thus rendered conductive, there is a substantial plate current owing. in the plate circuit of the tube I0, and since this plate circuit includes the resistor' 25, such substantial plate current flow produces a voltage drop across the resistance 25. This voltage drop is in addition to the voltage drop -due to the flow of plate current to the B-voltage connection 2I through the resistor 22. The voltage drop across the resistor affords a positive voltage at the juncture of the resistors 24 and 25, and this voltage is, of course, applied through the wires 38 and 36 to the cathode IIC of the control tube. This positive lvoltage is of a greater magnitude than the positive voltage that is applied throughy the resistor 40 to the grid IIG. Thus, the grid IIG under such conditions is suiciently negative with respect to the cathode IIC so that the tube `II is maintained nonconductive.Y It Awill be evident, of course, that since the tube II is non-conductive under such circumstances, there will be no current flow in the plate circuit of the tube II, and hence,

Ythere will be no voltage drop across the resistor 2li,` this condition being important in governing the vconductivity of the main amplifier tube I0, as will hereinafter becomeA apparent. It will be evident, therefore, that so long as the tube II remains non-conductive, the normal bias on the amplifying tube I0 will be maintained, and the signal received from the' receiver I5 will be amplified by the tube Ill and transmitted to the audio output.

When it is desired to render the amplifying tube I0 non-conductive, as Where a commercial announcement or the like is to be transmitted from the broadcasting station, a momentary cutout control signal of an inaudible frequency is transmitted on the carrier wave, and this con- ,trol signal has the frequency that corresponds with the resonant frequency of the tank circuit 10.. Thus, in the present instance,'such a control signal would have a frequency of 20 kc. This 20 kc. control signal would thus be applied to the grids of both of the amplifying tubes IOVand I2, but its .effective work is accomplished through V means including the amplifying tube I2. Thus,

the amplied 20 kc. signal is transmitted through the wire 55 and condenser 56 to the grid I IG, and this 20 kc. signal will, of course, be resonant in the tank circuit 10. The peak positive voltages of the 20 kc. signal that is thus resonated in the tank circuit 10 will be effective on the grid IIG, and with the circuit values above set forth, the positive voltage peaks of the resonated. signal will vbemore positive than the positive voltage applied to the cathode I IC through the wires 38 and 36, hence will serve to render the tube II conductive. This conduction by the tube II serves to"cause a pulsating direct current to flow in the plate circuit of the tube II, and the alternating the condenser 34 so that a direct current will flow 'in the platecircuit of the tube I I. This plate circuit includes the resistance 28 and the resistances 23 and 22, and by reason of the current flow in and throughthe resistor 28, a voltage drop is developed across the resistor 28. This allords additional negative bias that is applied to the control grid IIG of the amplifier tube Il), thereby to render the tube I non-conductive. This takes place during the relatively short period when the kc. control signal is being transmitted, and as soon as the tube I0 has become non-conductive, its plate current disappears and the voltage drop across the resistor is reduced below the value that is necessary as hereinbefore described to maintain the tube I I in its non-conductive state. Hence, when the 20 kc. control signal is terminated, the control tube I I remains conductive, and this serves to maintain the amplier tube I0 in its non-conductive state. Thus, the signal that is being applied to the grid of the amplifying tube ID will not again be amplined and transmitted to the audio output until the tube II has been rendered non-conductive.

When the commercial announcement or the like has been completed, and it is again desired to render the amplifier tube l0 conductive, a different frequency inaudible signal is momentarily transmitted on the carrier Wave that is being received by the receiver l5. This signal may be termed a restoring signal, and with the values hereinabove set forth, such restoring signal would have a frequency of kc. Such a 35 kc. restoring signal is, of course, applied to the grid of the amplifying tube I2, and the amplied output of the tube I2 is effectually applied to the 35 kc. tank circuit 62. This, of course, develops a voltage which is rectified in the rectifying tube I3, and this rectied output appears at the plate or anode I3A as a negative-going voltage that is applied through the Wires 68 and 6T, the resistance 68, the element 'I2 and the wire 'I3 to the grid I IG of the tube II. By negative-going voltage We mean a voltage that is becoming more negative, or less positive. This negative-going voltage serves to bias the tube II so that the plate current in the tube II is sharply reduced. This reduces the voltage drop across the resistor 28 to such a point that the tube I0 is again rendered conductive. The flow of plate current in the tube I0 then causes voltage drop across the resistor 25 which acts to bias the tube I I to cut-01T, as previously described. By reason of the continued current oW in the plate circuit of the tube Iii, the bias of the tube II to its cut-oil relationship is maintained so that upon termination of the 35 kc. restoring signal the amplifying tube I 0 remains in its conductive condition wherein the signal from the radio rece-iver I5 Will be continuously amplified and supplied to the audio output.

From the foregoing description it will be evident that the present invention enables commercial announcements or the like to'be eliminated from the reproduced program material at selected amplifiers, and enables this to be accomplished in a simple and expeditious manner. It Will be apparent also that such control is attained under the present invention through the use of relatively short control signals that need to be transmitted only at the beginning and the end of a period during which the amplier is to be disabled. The present invention also enables dif- 6 ferent frequencies `to disable `and to restore Athe amplier.

We claim:

l. In :anelectron'ic amplifier, a main` amplifier tube embodying a control grid adapted for connection to a signal source and also having an anode and a cathode and having a load circuit affording an audio `output connection, said load circuitincluding a plurality of resistors connected in series with said cathode, a grid bias connection including an additional resistor and the oneof said resistors that is adjacent said cathode, a .control tube having a grid, an anode and a cathode, a load circuit for said control tube including a connection from the anode of said control tube through'said one resistor and said additional resistor and a connection from the cathode of said control tube to a point on the load circuit of said main tube at which during current iiow in such last mentioned load circuit has a positive voltage of at least a predetermined magnitude, means operable to apply to the grid of said control tube a constant positive voltage of a magnitude less than said predetermined magnitude, a governing amplier tube having a load circuit and having a control grid adapted to be connected to a signal source, means connecting said last mentioned load circuit with said grid of said control tube and including a rst tank circuit tuned to resonance at a Iirst selected frequency, means including a second tank circuit tuned to resonance at a second frequency and connected between said last mentioned load circuit and ground, a rectifying tube having a load circuit operatively connected to said second tank circuit to rectify the output of said second tank circuit, and means connecting said grid of said control tube to said load circuit of said rectifying tube at a point, which during such rectifying action of said rectifying tube, has a negative-going voltage efective to reduce the current ow in the load circuit of said control tube and thus return said main amplifying tube to a conductive state,

2. In an electronic ampliier, a main amplifier tube embodying a control grid adapted for connection to a signal source and also having an anode and a cathode and having a load circuit affording an audio output connection, said load circuit'l including a plurality of resistors connected in series with said cathode, a grid bias connection for said grid including an additional resistor and the one of said resistors that is adjacent said cathode, a control tube having a grid, an anode and a cathode, a load circuit for said control tube including a connection from the anode of said control tube through said one resistor and said additional resistor and also including a connection from the cathode of said control tube to a point on the load circuit of said main tube which during current flow in such last mentioned load circuit has a positive voltage of at least a predetermined magnitude, means operable to apply to the grid of said control tube a constant positive voltage of a magnitude less than said predetermined magnitude, means for rendering the bias on said control tube positive to initiate conduction in said control tube, and means for reducing the positive bias on said control tube for rendering said control tube non-conducting.

3. In an electronic amplifier, a main amplifier tube embodying a control grid adapted for connection to a signal source and also having an anode and a cathode and having a load circuit affording an audio output connection, said load circuit including a plurality of resistors connected in series with said cathode, a grid bias connection for said grid including an additional resistor and the one of said resistors that is adjacent said cathode, a control'tube having a grid, an anode anda cathode, a load circuit for said control tube including a connection from the anode of said control tube through said one resistor and said additional resistor and also including a connection from the cathode of said control tube to a point on the load circuit of said main tube at whicht during current flow in such last mentioned load circuit has a positive voltage of at least a-.predetermined magnitude, means operable to apply to the grid of said control tube a constant positive voltage1 of a magnitude less than said predetermined magnitude, bias-changing means control tube for sharply reducing the current flow in said control tube.

NATHANIEL FEINER. SAMUEL H. GERSHATERJ.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date i l15 2,250,596 Mountjoy July 29, 1941 2,507,432 Bass May 9, 1950 

